Bladder cancer is the fourth most common cancer in men and eleventh most common in women. Approximately 80% of the cases are classified as superficial cancer and most are treated with surgery alone. However, 70% of newly diagnosed patients suffer disease recurrence after surgical treatment. Therefore, the development of efficient therapeutic countermeasures against this pathology is a high priority.
The bladder displays unique characteristics and challenges as an organ to be targeted for therapy. Specifically, bladder epithelial cells lining the luminal surface, known as umbrella cells, are engaged in tight junctions that prevent access to the lower transitional cell layers. Furthermore, umbrella cells express characteristic extracellular proteins (uroplakins) that assemble into semi-rigid plaques that effectively shield the apical surface. The urothelium is further isolated from the bladder lumen by a mucin layer comprised of GlycosAminoGlycans (GAG) that are produced and assembled on the apical surface of the umbrella cells. In addition, the well-differentiated umbrella cells have limited secretory and endocytic capacity. In contrast, malignant bladder cells are usually less differentiated and polarized, exhibit diminished uroplakin expression and low GAG layer synthesis. Therefore, as opposed to normal bladder epithelia, neoplastic cells are exposed to the lumen of the bladder. This leads to increased accessibility of tumor lesions to therapeutic agents, compared to the well-protected normal regions of the bladder. However, constant urine influx and periodic voiding of the bladder makes the direct instillation of therapeutic drugs limited in their impact on bladder tumor cells.
At present, intravesical instillation of live Mycobacterium bovis bacillus Calmette-Guerin (BCG) is currently the adjuvant therapy of choice for the treatment of superficial bladder tumors. While the specific mechanisms of BCG-mediated antitumor activity is not yet fully understood, direct targeting and binding to bladder tumor cells, followed by cellular uptake and subsequent activation of adaptive immune responses, are required. Nevertheless, intravesical BCG is associated with high local morbidity and a risk of systemic mycobacterial infection. Notably, multiple instillations leads to increased toxicity, thus limiting patient tolerance for the treatment regimen required for effective anti-cancer activity. Therefore, the development of high-affinity, non-toxic targeting strategies is of high priority in the field.
A breakthrough came from the identification of BCG's Fibronectin Attachment Protein (FAP) as the targeting molecule used by the bacteria to adhere to bladder tumor cells (Ratliff et al. Infect Immun 1993; 61: 1889-94; Schorey et al. Mol Microbiol 1996; 21: 321-9; and Schorey et al. Infect Immun 1995; 63: 2652-7). FAP was shown to interact with α5β1 Integrin-bound fibronectin (FBN) and undergo internalization by tumor cells. Since FAP by itself was observed to mediate antitumor activity in FAP-immune mice (Sinn et al. Cancer Immunol Immunother 2008; 57: 573-9), it may represent a lower-risk alternative to BCG for therapeutic purposes. In addition, the internalization of FAP by bladder tumor cells provides a novel and potentially powerful approach for the delivery of therapeutics that may greatly enhance the antitumor effect of FAP.
In accordance with the present disclosure a FAP-targeted delivery strategy is provided for delivering and inducing the uptake of cytotoxic agents into bladder tumor cells.